Five major executives abruptly left Twitter in a surprising Sunday-night shakeup. The social media giant’s heads of product, media, engineering, and Vine are no longer with the company, according to Re/code and the New York Times. The move is a massive and unexpected shakeup for the social media company that was once the darling of the tech world but lately has found its stock price plummeting and its position in the world of online media on unstable footing as social media companies like Snapchat, Instagram, and Facebook increasingly encroach onto Twitter’s role as media messenger.

Re/code first reported that Twitter’s head of media Katie Jacobs Stanton and head of product Kevin Weil are departing the company. Neither have reportedly landed at another company yet and their jobs at Twitter will be filled with interim replacements for the time being. Weil’s biggest product launch at Twitter was its new Moments feature, the roundup of news relating to a certain event—departing from Twitter’s reverse chronological timeline layout. In October returning CEO Jack Dorsey said "Moments represents a real shift in our thinking."

That shift in thinking has also seen the company seriously consider raising its 140-character tweet limit to 10,000 characters.

Then, the New York Times quickly followed up this afternoon, reporting that Twitter’s senior vice president of engineering Alex Roetter will also leave the company. It is also believed that Jason Toff, head of Vine, has left as well.

Re/code reports that Twitter will officially announce the departures tomorrow, as well as announce the hire of a new "prominent" CMO. Though it’s not known for sure who the CMO is, Re/code says "she was a well-known exec from a big brand company."

Now Mashable is reporting that a major Twitter investor has confirmed that the departures were the result of a long-planned restructuring. The source revealed that four of the executives who have left were allies of former CEO Dick Costolo and "were not people in whom Jack has the highest faith," according to Mashable.

For the time being, Twitter has declined comment on the reports. In addition to the five high-profile departures today, Re/code says that more changes are yet to come, "including an expected turnover on its board in the next quarter." The site also reveals that Twitter is expected to announce a new head of PR—something that perhaps can’t come soon enough.

Update: Twitter CEO Jack Dorsey has posted a block text tweet on his Twitter account commenting on the departures. Dorsey confirmed the departures of four executives, revealing that Twitter’s VP of human resources Brian Schipper is leaving the company as well. Dorsey said all of the exiting execs had "chosen to leave" the company.

Dorsey also revealed that in the interim Twitter COO Adam Bain will take on additional responsibilities including running the revenue-related product teams, as well and the media and HR teams. Current Twitter CTO Adam Messinger will take on consumer product, design and research, and user services.